The present invention pertains to a novel vector and more particularly to vectors having an insertion site in phase with three reading frames downstream of the promoter of alkaline phosphatase gene (phoA) of Escherichia coli. In order to produce foreign proteins extracellularly by recombinant DNA technology, the present inventors have cloned DNA fragments containing the promoter sequence, the Shine-Dalgarno sequence (SD sequence) and the signal sequence of phoA and determined its base sequence. Thus it became possible to strongly express a desired polypeptide by linking a gene coding for desired peptides downstream from the phoA promoter. Also a method for excreting a desired peptide or polypeptide was provided by linking a gene coding for the peptide or polypeptide in phase with the signal sequence of phoA by adjusting the reading frame as is described in U.S. Patent Application Ser. No. 435,456, now abandoned, filed Oct. 20, 1982.
Many restriction sites became available for insertion of a desired gene as the result of the determination of the base sequence and the construction of the restriction map of the phoA fragment. Nevertheless, improvements to the phoA expression vector were considered desirable. To this end, versatile expression vectors have now been constructed which have insertion sites cleavable with common restriction enzymes and which are in phase with any of the three reading frames of an inserted gene.